Disclosed is a cured form of calcium silicate, mainly comprising tobermorite and exhibiting a powder X-ray diffraction pattern in which the diffraction peak intensity Ib ascribed to the (220) plane of the tobermorite and the minimum diffraction intensity Ia observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite satisfy the relationship Ib/Ia3.0; a differential pore distribution curve obtained by mercury porosimetry in which the logarithmic width of the pore diameter distribution as measured at a height of of the height of the maximum peak of the differential pore distribution curve is from 0.40 to 1.20, and also disclosed is a reinforced calcium silicate composite structure, and methods for producing same. The cured form of calcium silicate and the reinforced calcium silicate composite structure of the present invention which, while exhibiting an apparent specific gravity of from 0.14 to 1.0 (and, hence, having a light weight), exhibit excellent properties as a building material, such as a high strength, a high modulus of elasticity, a high resistance to the neutralization reaction, a high dimensional stability, and a high resistance to chipping.